Currently, physicians typically monitor a number of systemic (e.g. the macrocirculation) hemodynamic parameters when diagnosing and monitoring of the hemodynamic condition of patients. For example, blood flow and pressure are regularly monitored. In addition, a blood sample may be withdrawn from the patient to determine the oxygenation of the red blood cells as well as the oxygen carrying capacity of the circulating blood. Furthermore, a biopsy may be required to determine the functional state of tissue cells (e.g. the oxygenation and viability of tissue cells) of the organ system.
While monitoring these macrohemodynamic parameters has proven successful in diagnosing and monitoring a number of conditions, several shortcomings have been identified. For example, examining macrocirculatory parameters provides little or no information relative to the microcirculatory (i.e. hemodynamics and structure of blood vessels smaller than 250 microns) characteristics of patients. Current research has shown that distress at the microcirculatory level involved in a large number of disease states is not discoverable by monitoring macrocirculation. As such, diseases or other complications evident through microcirculatory monitoring may go undetected and untreated.
It is believed, for example, that improved clinical observation of the microcirculation of human organs would be extremely useful in assessing states of shock such as septic, hypovolemic, cardiogenic and obstructive shock in patients and in guiding resuscitation therapies aimed at correcting this condition. In particular, it has been found that the active recruitment of the microcirculation maybe an important component of resuscitation. Additionally, improved clinical observation of the microcirculation would be helpful in observing gross circulatory abnormalities in pathologies such as tumors and cardiovascular disease.
To fully monitor the function of the microcirculation, that is the structure and perfusion of vessels smaller than 250 micrometers, in addition to measuring blood flow it is important to measure and asses whether the blood cells are successful in transporting their oxygen to the microcirculation and thereafter to the surrounding tissue cells. Of particular importance is the assessment of the perfusion of the capillaries, which are between approximately 5 to 10 micrometers, because it is at this level that oxygen is transported by the red blood cells to the tissue cells of the organ for the purposes of respiration and survival. Monitoring the functional state of the microcirculation can thus be regarded as monitoring the ultimate efficacy and function of the cardiovascular system to deliver adequate amounts of oxygen to the organ cells.
It is believed, for example, that improved and comprehensive imaging of the properties of the microcirculation would be helpful in observing and assessing the beneficial effects of therapy during the resuscitation of shock patients. An accurate assessment of both blood flow and oxygen availability at the level of the microcirculation could thus provide a clinical tool with which to guide resuscitation. A comprehensive way to monitor the microcirculation could generally provide an improved clinical diagnostic tool for evaluating and monitoring the functional state of the microcirculation in the peri-operative phase of treatment.
To date, there have been limits to a comprehensive monitoring of the microcirculation in order to provide the benefits discussed above. Specifically, several factors have limited the ability to evaluate the oxygen transport variables of the microcirculation comprehensively. For example, devices which contact the surface of the microcirculation inhibit their ability to obtain quantitative information about blood flow in the various categories of micro-vessels in the microcirculation by impeding flow due to exerted pressure. Furthermore, current devices and techniques for imaging the microcirculation do not provide the additional needed information about the oxygen availability in the microcirculation or about the adequacy of oxygenation of the tissue cells. This information would be very helpful in assessing the functional state of the microcirculation, specifically its function in allowing adequate transport of oxygen to the tissue cells. Thus, there is a need for an improved system and method for a more effective and a more comprehensive clinical observation of the microcirculation which includes these parameters.